The screening of diamonds (and other gemstones) is required in order to distinguish synthetic materials from those that are natural. It is known that, in an unpolished state, High-Pressure, High-Temperature (HPHT) synthetic diamonds have distinctive cubo-octahedral shapes which make them easy to distinguish from natural diamonds which grow in an octahedral form. Even when synthetic material is polished into a gemstone, identification is still possible. In certain cases, identification can be adequately performed by looking for metallic inclusions and colour-zoning (where colour is more concentrated in certain geometric zones) using a microscope. However, in order to identify synthetics having better quality and colour more advanced instrumentation such as the Applicants' DiamondSure™ and DiamondView™ instruments may be required.
The DiamondSure™ instrument is a rapid, easy to use, screening instrument which measures the way light is absorbed by a diamond in order to identify synthetics. The diamond under test may either be passed, if it is a natural, or referred for further tests, if the stone needs to be looked at more closely. It has been found that this instrument refers all synthetics and around 2% of natural diamonds (which are susceptible to a colour treatment) for further testing.
The referred diamonds are then analysed using the DiamondView™ instrument which generates a surface fluorescent image of the stone using intense short-wave ultraviolet lamps. As synthetics typically show distinct geometric patterns from their characteristic growth sectors, these can quickly be identified.
However, as the diamonds are required to be in a particular orientation for each of the above screening processes, it has, to date, been necessary for each individual diamond to be manually placed on the screening equipment. There is therefore a need for automatic gemstone orientation in order to speed up this procedure.